To form PTFE into long shapes (such as tape) a paste-extrusion method was developed. A hydrocarbon lubricant is added to the fine powder PTFE and allowed to equilibrate. The amount of lubricant must be controlled to equal the free volume of the powder upon compacting in a performing press, typically 16-24% of the weight of the polymer. A high amount of lubricant results in an incomplete coalescence of particles during compacting, whereas a low amount of lubricant results ina high extrusion pressure. The paste form can then be extruded through a tapered die at higher pressures to form tubing, rods, or wire coatings. The formed object is then heated carefully to drive off the lubricant, after which it is heated strongly to sinter the resin. The high-melt viscosity of PTFE allows even unsupported shapes, such as tubing, to be sintered without loss of shape in this last step. Properties and Applications PTFE is a white solid with waxy appearance and feel. It is a tough flexible material of moderate tensile strength
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